Pneumatic, rotary, rack type actuators are known and widely used for converting the reciprocating movement of two opposing rack and piston assemblies into reciprocating rotary movement of a drive shaft. Such rack type pneumatic actuators are known for example from U.S. Pat. No. 3,447,423.
In pneumatic rack-type actuators of the kind mentioned above, it is necessary to adequately slow down and dampen the reciprocating movement of the rack and piston assemblies each time their strokes are reversed, to prevent shocks and damages. Currently, use is made of hydraulic decelerating or damping systems which are mounted outside the actuator using complex and cumbersome solutions which involve additional costs; from U.S. Pat. No. 3,447,423 it is also known the use of a throttling valves comprising pin members arranged on the pistons to enter an inlet port restrict flow of fluid as the piston assemblies approach the ends of their strokes.
In the field of pneumatic actuators it is also known the uses of pneumatic damping devices which intervene at the end of the stroke performed by the piston assembly and which operate on the principle of air compression, with extremely limited damping efficiency and without providing any possibility of controlling the damping effect. In fact, in pneumatic damping devices of the known type, the chamber intended to be subjected to a counter-pressure is normally open or vented to the atmosphere, being closed by the said piston only at the end of its stroke. Therefore, allow air pressure is established in said chamber at a value substantially close to atmospheric pressure and must be compressed by a "pumping" action of the piston, before the latter reaches the end of the stroke resulting in a very limited or inefficient damping and decelerating effect; otherwise extremely long and additional stroke of the piston would be necessary, resulting in a considerable increase in the dimensions as well as the costs of the actuator.
From FR-A-2.200.451 a fluid operated actuator it is known in which a pressurized chamber of a cylinder is brought in communication with an opposite pressureless chamber of the same cylinder by pin actuated valve members provided in a lateral passage of the piston, to be actuated at the approaches of the end of the strokes of the same piston; nevertheless in said actuator, the low pressure chamber is usually vented or connected to a discharging duct and no positive counter-pressure control or controlled dumping actions are possible when the piston assembly approaches and is moving towards the end of it stroke. Therefore, the pneumatic damping devices currently known are difficult to use or to adapt for applications on rack-type rotary actuators, or are not able to provide a positively controlled damping action.
Currently, rack-type rotary actuators incorporating pneumatic damping and controlled decelerating systems, able to satisfy the abovementioned requirements, are not known.
Therefore, the general object of the present invention is to provide a pneumatic rotary actuator of the pinion and rack type, provided with differentiated pneumatic damping actions, to dissipate the accumulated energy by means of a counter-pressure positively generated at a required moment and in a controlled manner, within the same actuator, in an extremely small space at the approaching end of each working stroke, successively allowing a low-down to stop and reverse the sliding movement of the rack and piston assemblies.
A further object of the present invention is to provide a rack-type rotary actuator provided with an internal, pneumatic, counter-pressure damping device, as mentioned above, having a very low cost and by means of which it is possible to achieve a high damping and decelerating effect, with high counter-pressure values, equivalent or close to the pressure value of the operating fluid of the same actuator.
A further object of the present invention is to provide a pneumatic rotary actuator of the rack type, by means of which it is possible to control both the instant when the deceleration phase starts and the value of the counter-pressure required to dissipate entirely the accumulated energy, whilst keeping the overall dimensions very compact and substantially equivalent to the useful working stroke of the said actuator.
A further object of the present invention is to provide a rotary pneumatic actuator of the rack type, by means of which it is possible to continuously adjust the working stroke or to obtain a programmable intermediate stopping position, whilst maintaining the desired damping effect.